Not applicable
Not applicable
1. Field of the Invention
This invention relates to a microlithographic reduction objective, and more particularly to a purely refractive high power objective, as is required for high resolution microlithography, particularly in the DUV wavelength region.
2. Discussion of Relevant Art
Such refractive objectives with two beam waists have already been described in the article by E. Glatzel, xe2x80x9cNew Lenses for Microlithographyxe2x80x9d, SPIE, Vol. 237, 310 (1980), and have been constantly developed since then. Objectives of the category concerned, of the Carl Zeiss Company, are sold in PAS wafer steppers and wafer scanners of the ASML Company, Holland.
Such an objective made by the Tropel Company in 1991 is shown in FIG. 16 of J. H. Bruning, xe2x80x9cOptical Lithographyxe2x80x94Thirty years and three orders of magnitudexe2x80x9d, SPIE, Vol. 3049, 14-27 (1997). Numerous variants of projection objectives of the category concerned are found in patent applications, such as European Patent applications EP 0 712 019-A (U.S. application Ser. No.08/337,647 of Nov. 10, 1994), EP 0 717 299-A, EP 0 721 150-A, EP 0 732 605-A, EP 0 770 895-A (U.S. Pat. No. 5,781,278), and EP 0 828 172-A.
Similar objectives with a somewhat smaller numerical aperture are also found in Russian Patent SU 1 659 955-A, EP 0 742 492-A (FIG. 3), U.S. Pat. No. 5,105,075 (FIGS. 2 and 4), U.S. Pat. No. 5,260,832 (FIG. 9) and German Patent DD 299,017-A.
The present invention has as its object to provide a type of objective which, in the context of the present state of the art, is outstanding for its high resolution with a large image field and small overall length, and its correction of imaging errors, particularly as regards distortion, remains stable even with different kinds of illumination (different degrees of coherence, etc.) and with significant stopping down (for exposure with large depth of focus region).
The object is attained with a microlithographic projection objective with a lens arrangement, having a first lens group (LG1) of positive power, a second lens group (LG2) of negative refractive power, a third lens group (LG3) of positive refractive power, a fourth lens group (LG4) of negative refractive power, and a fifth lens group (LG5) of positive refractive power. The numerical aperture on the image side is greater than 0.65, preferably 0.68. A system diaphragm (AS) is situated in said fifth lens group (LG5). And, at least two lenses of said fifth lens group (LG5) are situated before said system diaphragm (AS).
It is advantageous that said fifth lens group (LG5) has at least 13 lenses (L18-L31).
It is also advantageous that the first lens group (LG1) of positive refractive power forms a convexity (B1) of a pencil of rays, the second lens group (LG2) of negative refractive power forms a waist (T1) of said pencil of rays, the third lens group (LG3) of positive refractive power forms a second convexity (B2) of said pencil of rays, the fourth lens group (LG4) of negative refractive power forms a second waist (T2) of said pencil of rays, and the fifth lens group (LG5) of positive refractive power forms a third convexity (B3) of said pencil of rays.
The system diaphragm (AS) is in a region of a lens (L22) at which said pencil of rays assumes its greatest diameter and its two neighboring lenses (L21, L23).
The diaphragm is placed in the fifth lens group in the region of the third convexity of the pencil of rays. This fifth lens group and the incorporation of the system diaphragm altogether has more importance. The attention paid partially in the state of the art to the configuration of the waists, especially the first, is then quite unimportant, as the embodiments show.
The high numerical aperture as the primary means for attaining high resolution strains the design, essentially between the system diaphragm and the image plane, particularly when the overall length and the lens diameter have to remain small in some degree, which is strongly preferred, particularly for easy integration into an existing design of a projection exposure equipment and for production, and also on grounds of cost.
A particularly advantageous capability of stopping the objective down, which is attained by respective independent minimizing of the various image errors is made possible by the design conception of the invention. This is in contrast to a fixed aperture objective, in which various large errors can be subtractively averaged out. The advantage is that the user can optimize the trade-off of resolution and depth of focus, respectively in relation to the case of application.
The production process according to the invention makes use of the outstanding correction of the objective by flexible illumination setting and aperture setting with different successive exposures in the production process. The individual exposures can in this case take place with different masks in a single projection exposure equipment, or several projection exposure equipments according to the invention, or also in combination with others, can be used in a production line.